Dielectric resonator elements are used in oscillators and filters as the frequency adjustment elements for narrow-band frequencies in the microwave and millimeter wave bands. Dielectric resonator elements are small in size, and have high Q values In addition, the resonant frequency of dielectric resonators is insensitive to temperature fluctuations. Accordingly, such resonators are being used on a rapidly-increasing scale in satellite communication devices, mobile radio devices, variable-frequency oscillators, and other applications.
While a dielectric resonator having a high Q value provides a stable resonance frequency, its resonance frequency cannot be widely varied electronically. Instead, its resonance frequency is varied mechanically, such as by mechanically varying the cavity size. However, mechanical adjustments change the resonance frequency slowly, and are bulky and expensive.
In one form of communication referred to as Minimum Shift Keying (MSK), data is sent by using two different frequencies to represent the binary data values 0 and 1, respectively. This system requires an oscillator whose frequency can be rapidly changed. The rate at which data can be transmitted in this system depends on the difference in frequency used to transmit the two data states.
Systems that allow the oscillator frequency to be shifted in response to a signal are known to the art. For example, unexamined Japanese Patent Publication No. HEI 9-205324 discloses a system in which the resonance frequency of an oscillator is altered by applying a signal to a variable capacitance element in an auxiliary transmission line. The magnetic field in the resonating element is coupled to the magnetic field of the auxiliary transmission line in this system. By altering the magnetic field, this device alters the resonant frequency. Generally, the variation in the resonance frequency is limited to about 0.1% of the resonance frequency. Hence, when a resonator of this type is used to construct a voltage-controlled oscillator that oscillates in the 5 GHz band for MSK communications, the oscillation frequency can only be varied by about 5 MHz. This limits the data transmission rate to about 10 Mbps. However, speeds exceeding 20 Mbps are sought for 5 GHz band radio communications.
Broadly, it is the object of the present invention to provide an improved dielectric resonator.
It is a further object of the present invention to provide a resonator whose resonance frequency can be shifted in response to an external electrical signal.
These and other objects of the present invention will become apparent to those skilled in the art from the following detailed description of the invention and the accompanying drawings.